The present invention relates to a paper guide, which is arranged on an upstream side of an electrostatic latent image carrier and forms a paper transport path between registration rollers and pre-registration rollers.
For reasons related to installation space, mainstream image forming apparatuses of recent years have been of a space-saving vertical carrying type. That is, these are structured such that a plurality of paper supply cassettes are arranged stacked in a lower portion of the apparatus main unit and a transfer portion and a fixing portion are arranged in an upper portion thereof. In these structures, a carried sheet that has been supplied from the paper supply cassette is initially carried upward then carried toward the transfer portion after being changed to horizontal direction carrying by being bent substantially 90 degrees before the transfer portion.
FIG. 9A shows a configuration of the paper transport path on a front side of the transfer portion.
Pairs of carry rollers R31 and R32, pre-registration rollers R41 and R42, and registration rollers R51 and R52 are arranged in order along a sheet carry direction S of a paper transport path 28, which is arranged in a bent shape as mentioned above, and the registration rollers R51 and R52 are provided facing a nip portion N5 with a distance of approximately 50 mm, the nip portion N5 being a contact portion between an electrostatic latent image carrier (photosensitive drum) 14 and a transfer roller 17a. Furthermore, a guide member 80, which is constituted by an upper paper guide 81 and a lower paper guide 82 and forms the paper transport path, is fixedly arranged having a constant interval and in a slightly upwardly bent state between the registration rollers R51 and R52 and the pre-registration rollers R41 and R42. That is, as shown in FIG. 11, the upper paper guide 81 and the lower paper guide 82 are structured such that both their end portions are fastened by screws 98 or the like.
FIG. 10 is a chart showing an operation timing of the registration rollers R51 and R52 and the pre-registration rollers R41 and R42.
Namely, when paper P is carried on the paper transport path 28 until the registration rollers R51 and R52 and the paper leading edge contacts (is sandwiched by) a nip portion N5 of the registration rollers R51 and R52, the registration rollers R51 and R52 first stop at a time t1 then at a slightly subsequent time t2, the pre-registration rollers R41 and R42 stop. Due to stopping with this time gap, the paper P that is sandwiched by the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 is held in a flexed state in a slightly bent form as shown in FIG. 9A. At this time, as shown in FIG. 9B, variation in a run-out amount L1 of the paper P from the nip portion N5 of the registration rollers R51 and R52 occurs due to such factors as the paper size, thickness, paper strength, and the balance of pressing force between the registration rollers R51 and R52.
After this, the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 again commence carrying of the paper P at a time t3, which is a timing that enables the leading edge of the paper P and the leading edge of image information that is developed on the electrostatic latent image carrier (photosensitive drum) 14 to correspond. By causing the paper P to be flexed slightly at this time, the feed timing for the leading edge of the paper P from the registration rollers R51 and R52 can be made consistent along the width direction of the paper, thereby preventing slanted carrying of the paper P and eliminating width direction deformation of the image to be formed on the paper P. That is, the paper P that is temporarily stopped by the registration rollers R51 and R52 undergoes during the stoppage fine adjustments of leading edge positions in the direction parallel to the paper transport direction S, center alignment of the carried paper, and correction of slanted carrying at the time of carrying by the registration rollers R51 and R52.
At this time, when the paper P is subjected to slanted carrying, amounts of flexure of the paper P vary at the left and right edges of the paper P orthogonal to the carrying direction S. In an example shown in FIG. 12 (FIG. 12A and FIG. 12B), a flexure amount A (see FIG. 12A) of the paper P is large on an back side of the paper transport direction (the right side when viewing the paper transport direction from the upstream side to the downstream side) and a flexure amount B (see FIG. 12B) of the paper P is small on a front side of the paper transport direction (the left side when viewing the paper transport direction from the upstream side to the downstream side). In this manner, due to the paper P being subjected to slanted carrying, a portion where the paper P makes contact with the paper guide arranged at a fixed spacing as well as a portion where the paper P does not make contact are produced on the paper P.
It should be noted that JP 2003-276900A also gives description in regard to a paper guide structure. A buffer mechanism portion that is constituted by an elastic force producing member, which is swingable and capable of absorbing slack and tension of the paper, and a paper guide is provided in the above-mentioned JP 2003-276900A, and it is described that in this buffer mechanism portion there is a structure provided with the elastic force generating member for absorbing slack and tension of the paper and an oscillation suppressing spring for achieving oscillation suppression that acts in an opposite direction, and the paper guide carries out a rotation movement centered on a shaft.
Incidentally, when the paper guide is fixedly arranged with a fixed spacing as mentioned above, a considerable load is exerted on the contact area due to the flexure amount of the paper in regard to the area where the paper makes contact with the paper guide due to the flexure caused by slanted carrying. For this reason there is a likelihood that problems such as the following will occur.
Namely, (1) the paper will be subjected to frictional electrification such that an uneven frictional electrification electric potential is produced in a single paper. (2) Paper dust will be generated from the paper due to abrasion at the contact area. (3) Correction of slanted carrying will not be able to be carried out correctly due to increased local loads from the paper guide. (4) Wrinkling or the like will occur due to twisting of the paper by slanted carrying.
These problems are causes of reduced printing quality in subsequent processing of the carried paper and deterioration of consumables (the photosensitive body, developer and the like).
The present invention has been devised to address these problems and it is an object thereof to provide a movable paper guide of an image forming apparatus that eliminates the various above-described problems that occur due to the rubbing between the paper guide and the paper, by allowing one of the upper and lower paper guides arranged between the registration rollers and the pre-registration rollers to have a movable structure capable of absorbing “paper flexure” that is produced to correct slanted carrying of the carried paper.